Sliding gate for liquid metal flow control

ABSTRACT

A metering gate for liquid metal flow control with reduced clogging with a top plate, having a first flow channel bore with an inlet having an inlet axis and an outlet having an outlet axis. The inlet axis and the outlet axis are offset. A throttle plate slidably mounted on the top plate selectably receives flow from the top plate. The metering gate provides a less tortuous and more symmetrical flow path when the gate is partially open, but provides a relatively straight downward flow channel allowing full flow when the gate is fully open.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to metal founding. More specifically, theinvention relates to a method and apparatus for metering liquid metalduring metal founding.

[0003] 2. Description of the Related Art

[0004] Metering gates with three plates are used to control the rate ofliquid metal flow exiting a teeming vessel, such as a tundish. Forexample, a metering gate may be used to control the rate of liquid steelflowing from the tundish of a continuous casting machine into a mold.

[0005] A metering gate consists of an assembly of refractory components,each of which has a flow channel. The flow channels (i.e. the holes orbores) within the refractory components are assembled together so as toprovide a complete flow channel through the gate, which is in fluidcommunication with the teeming vessel and through which the liquid metalmay be allowed to flow.

[0006] The refractory components of the metering gate are assembled andclamped together by mechanical means such that one component, a throttleplate, can slide laterally in the metering gate assembly to control therate of liquid metal flow through the gate. By sliding the throttleplate to various positions, the gate may be either closed, partiallyopen, or fully open to control the rate of flow exiting the teemingvessel.

[0007] Several problems are typically associated with controlling theflow of liquid steel exiting a tundish with metering gates. Theseproblems include: (1) bending of metal flow in the flow channels of thegate, which can cause excessive turbulence and asymmetrical discharge ofliquid metal; (2) severe non-uniform plugging of the flow channels fromthe accumulation of metallic and non-metallic materials which adhere tothe channel walls with a subsequent loss of ability to obtain thedesired rate and smoothness of liquid metal discharge; and (3) localizedand accelerated eroding of a refractory component of the metering gatewith subsequent contaminating of the liquid metal and potential loss ofcontrol or metal leakage.

[0008] Referring to FIGS. 1 and 2, a three-plate metering gate assembly10 (hereinafter “gate 10”) typically consists of five basic components:a well nozzle 20, a top plate 30, a throttle plate 40, a bottom plate 50and an outlet tube 60. Liquid metal (not shown) flows into gate 10 atthe top and flows out of gate 10 at the bottom.

[0009] The well nozzle 20 is a pipe, which allows the entry of liquidmetal flowing from the teeming vessel (not shown) into a flow channelbore 22 at the top of the well nozzle 20. The top plate 30 is in contactwith the bottom of well nozzle 20, and includes a flow channel bore 32.The central axis 35 of the flow channel bore 32 in top plate 30, asshown in FIG. 2, is collinear with central axis 25 of flow channel bore22 in well nozzle 20.

[0010] Throttle plate 40 is in contact with the bottom of top plate 30.Gate 10 is designed so that throttle plate 40 may slide laterallyrelative to the other components of gate 10. Bottom plate 50 is incontact with the bottom of throttle plate 40, and includes a flowchannel bore 52. Central axis 55 of flow channel bore 52 in bottom plate50 is collinear with central axis 25 of flow channel bore 22 in wellnozzle 20.

[0011] Outlet tube 60 is in contact with the bottom of bottom plate 50,and includes a flow channel bore 62. Central axis 65 of flow channelbore 62 in outlet tube 60 is collinear with central axis 25 of flowchannel bore 22 in well nozzle 20.

[0012] Central axes 25, 35, 55 and 65 of flow channels 22, 32, 52 and 62in well nozzle 20, top plate 30, bottom plate 50 and outlet tube 60,respectively, are collinear and all together define the “main centralaxis” 15 of gate 10.

[0013] As shown in FIGS. 3-5, throttle plate 40 slides between fullyopen (FIG. 3), partially open (FIG. 4) and gate closed (FIG. 5)positions. As shown in FIG. 4, during normal operations, throttle plate40 typically is placed in a partially open position so that the flowrate of liquid metal through gate 10 may be metered, i.e., set andcontrolled, at a desired rate. As shown in FIG. 3, throttle plate 40assumes a fully open position to maximize the flow of liquid metalthrough gate 10. As shown in FIG. 5, throttle plate 40 may assume aclosed position, which would stop the flow of liquid metal through gate10.

[0014] Metering gate components may be combined or subdivided. Forexample, to reduce the number of components, a gate 710 may be composedof only three parts, as shown in FIG. 6, in which the well nozzle may becombined with the top plate, defining a first component 712, and/or thebottom plate may be combined with the outlet tube, defining a secondcomponent 714, selectively placed in fluid communication with a throttleplate 740. As shown in FIG. 7, to more easily replace the outlet tube ofa gate 810 having a well nozzle 812, a throttle plate 813 and a bottomplate 814, the bottom plate 814 may be divided into two plates 816 and818.

[0015] Several variations of the fundamental three-plate gate componentsare used. For example, unlike the gate shown in FIGS. 1-5, in which wellnozzle 20 has a tapered conical section bore 22 and bores 32 and 52 inplates 30 and 50 and bore 62 of outlet tube 60 define simple cylinders,as shown in FIG. 8, a gate 110 may have a well nozzle 120 with acylindrical bore 122 and a top plate 130 with a conical bore section 132with the bores in the throttle plate 140, the bottom plate 150 and theoutlet tube 160 being the same as in the gate 110 of FIGS. 1-5. Also, asshown in FIG. 9, a gate 210 may have conical bore sections 222 and 232in both well nozzle 220 and top plate 230 with the bores in the throttleplate 240, the bottom plate 250 and the outlet tube 260 being the sameas in the gate 110 of FIGS. 1-5, and, as shown in FIG. 10, a gate 310may have a well nozzle 320 having parabolically-shaped bore 322 and atop plate 330 having a conically-shaped bore 332 with the bores in thethrottle plate 340, the bottom plate 350 and the outlet tube 360 beingthe same as in the gate 110 of FIGS. 1-5.

[0016]FIG. 11 illustrates another variation of a gate 410 wherecylindrical bore 442 in throttle plate 440 is canted at an angle toplate surface 443 in an attempt to direct the flow through throttleplate 440 back toward main central axis 415 of gate 410. FIGS. 12 and 13illustrate partially open and gate closed positions, respectively, ofgate 410.

[0017] In gate 410, bores 422, 432, 442, 452 and 462 in well nozzle 420,top plate 430, throttle plate 440, bottom plate 450, and outlet tube460, respectively, generally are axisymmetrical. For example, the boreshave either cylindrical or conical section geometry. The central axis425, 435, 455 and 465 of well nozzle 420, top plate 430, bottom plate450, and outlet tube 460 generally are collinear.

[0018] Other variations of metering gates have been developed to providefor better draining of the throttle plate when it is closed. Forexample, FIGS. 14-16 show a gate 510, including a well nozzle 520, a topplate 530, throttle plate 540, bottom plate 550, and outlet tube 560, inopen, partially open and closed gate positions, respectively. Gate 510is similar to that of FIGS. 1-5 except that throttle plate flow channelbore 542 is extended by a special drain cut 544 near bottom edge 546 onone side to allow draining of bore 542 when the gate is in the closedposition, as shown in FIG. 16. This prevents trapping of liquid metal inthrottle plate bore 542 which otherwise would solidify when the gate 510is temporarily closed.

[0019] FIGS. 17-19 show another gate 610, including a well nozzle 620, atop plate 630, throttle plate 640, bottom plate 650, and outlet tube660, in open, partially open and closed gate positions, respectively,which provides another drainage feature. A conical bore section 652, atthe top of bottom plate 650, has a diameter at top surface 654 of bottomplate 650 that is larger than the diameter of bore 652 at bottom surface656 of bottom plate 650.

[0020] Unfortunately, the foregoing gate designs all provide a tortuousliquid metal flow path when the gate is partially open—the normaloperating position during liquid metal pouring. Metering gates aredesigned with a maximum flow rate, but are intended to operate at about50% of that rate. This assures the desired gate control response andaffords excess capacity, which occasionally may be required forhigh-production or large section casting. Thus, a partially open gate istypical during liquid metal pouring, because the size of the flowchannel must be large enough to provide a sufficient opening toaccommodate a maximum rate of flow of the casting, but typically a gateis operated at less than maximum flow. The required or desired amount ofliquid metal flow through the nozzle typically varies during the castingoperation and generally is significantly less than the maximum, rangingfrom 30% to 70% of the maximum most of the time. As a result, the bentand contorted flow path formed in these gates when partially opencauses: (1) asymmetric discharge of the liquid metal; (2) excessiveturbulence in the flow channel; (3) localized regions which can besubject to accelerated erosion of refractory material; (4)over-restriction of the flow; and (5) rapid build-up of clogging incritical locations of the flow channel. The net effect is to shorten theuseful life of the gate components and increase operating cost.

[0021] The distorted flow generated by these gates when partially openis illustrated schematically in FIGS. 20 and 21 with gates 210 (FIG. 9)and 410 (FIGS. 11-13) respectively. In FIG. 20, flow 271 in flow channel212 impacts upper ledge 248 of throttle plate 240 (at Region A) whichbends this portion of flow 271 sharply toward the opening of bore 242.Flow 272, which is the remaining portion of the flow, is bent to a muchlesser degree. This mainly one-sided bending of the flow causes a flow273 to separate from the surface of throttle plate bore 242 below thetop edge 248 thereof and to be redirected toward bore 242. A highvelocity jet flow 274 formed in throttle plate bore 242 is tiltedstrongly away from main central axis 215 of flow channel 212. Thistilted jet impinges upon one side of bore 252 in bottom plate 250(Region B) and feeds fluid into recirculating flow 275 under the ledgeformed by the plate 230. The severe bending and tilting of the flowdescribed above produces an asymmetrical flow pattern in bottom plate250 and outlet tube 260 with: (1) a high speed flow 276 confined to oneside of flow channel 212; and (2) an extensive recirculating flow 277,including very turbulent portions 278 and 279 which occupy the majorportion of flow channel 212.

[0022] This flow behavior is deficient because it leads to excessivepressure loss and promotes clogging and erosion. The strong bending andtilting of the flow and its impingement on the refractory material (e.g.at Regions A & B), over-restricts the flow and the discharge of liquidmetal is more easily impeded by any build-up of clogging material.Recirculating flow 275 is fed with incoming fluid providing idealconditions for the build-up of non-metallic clogging material in bore242 of throttle plate 240, which is a critical problem for gateperformance. The asymmetrical nature of the flow in the outlet tube 260,with a concentrated jet 277 on one side and turbulent recirculation 279on the other side, causes: (1) asymmetrical discharge of liquid metalfrom outlet tube 260, which can detrimentally affect cast metal quality;and (2) non-uniform and rapid clogging of outlet tube 260. Impingementof the flow on the sides of bore 252, such as in Region B, alsoaggravates problems with localized refractory erosion.

[0023] Referring to FIG. 21, one attempt to direct the flow back towardmain central axis 415 of gate 410 fails and even exacerbates problemsrelated to the tortuous flow path and the asymmetrical nature of flowdistribution when gate 410 is partially open. FIG. 21 shows the flowpattern related to gate 410 having a canted cylindrical bore 442 inthrottle plate 440 and a conical section bore 452 in bottom plate 450.The flow pattern is similar to, but more asymmetrical than, the flow ofFIG. 20. Specifically, canted-throttle-bore flow 471 is bent moresharply where it impacts above top ledge 446 of throttle plate 440(Region A), while flow 472 is bent much less than flow 471. This isbecause, comparing FIGS. 20 and 21, with a canted cylindrical bore 442,the entry of bore 242 essentially is shifted rightwardly, effectivelypresenting a longer ledge 446 which urges the flow 471 more orthogonalrelative to the main central axis 415 than flow 271 interacting with asmaller top ledge.

[0024] The canting of bore 442 in throttle plate 440 also promotes alarger region of separated flow 473, as compared to FIG. 20, on one sideof bore 242 in throttle plate 240. High velocity flow 474 is tilted moreseverely away from main central axis 415 of gate 410 which impinges moredirectly on one side of bottom plate bore 452 (Region B). Increaseddirect impingement of the jet increases the proportion of recirculatingflows 475 and 476 under top plate ledge 446 and increases theconfinement of high speed flow 477 entering outlet tube 460 to one sideof flow channel 462. Subsequently, there is an increase in the extent ofturbulent flow 478, 479 and 480 on the other side of flow channel 462.Thus, discharge is over-restricted and flow asymmetry entering outlettube 460 is more severe, promoting clogging and erosion.

[0025] Accordingly, metering gate designs which attempt to improve flowsymmetry by angling or canting the flow channel in the throttle plate todirect the flow back toward the main central axis of the gate when thegate is partially open are deficient and can cause greater problemsduring operation.

[0026] The foregoing demonstrates a need for a metering gate thatpromotes a straight liquid metal flow path.

SUMMARY OF THE INVENTION

[0027] The invention provides a method and apparatus for metering flowincluding selectively passing fluid through a passage in a top plate,having an inlet and an outlet, wherein the inlet and the outlet areoffset, then into a throttle plate.

[0028] The invention provides for a metering gate which promotes astraighter liquid metal flow path and a more symmetrical and lessturbulent discharge, thereby reducing the potential for clogging anderosion of the gate components. The invention provides for a reductionin the extent of separated and turbulent flow regions when the gate ispartially open. The invention provides for less erosive flow behavior.The invention provides for less restriction when partially open, therebyallowing easier passage of the liquid metal. The invention provides forfewer clogging problems by retarding the rate of build-up, reducing theextent of build-up and improving the uniformity of any build-up. Theinvention provides for improved uniformity of flow distribution in theoutlet tube, thus improved metal flow behavior in a downstream vessel,such as a continuous casting mold. The invention provides for easierdraining of the throttle plate without detrimental effect on flowbehavior. The invention provides improved elements and arrangementsthereof, for the purposes described, which are dependable and effectivein accomplishing intended purposes of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention is described in detail below with reference to thefollowing figures, throughout which similar reference characters denotecorresponding features consistently, wherein:

[0030]FIG. 1 is a top plan view of a known metering gate in a partiallyopen position;

[0031]FIG. 2 is a sectional view, taken along line II-II in FIG. 1showing the metering gate in a partially open position;

[0032]FIG. 3 is a view showing the embodiment of FIG. 2 in a fully openposition;

[0033]FIG. 4 is a view showing the embodiment of FIG. 2 in a partiallyopen position;

[0034]FIG. 5 is a view showing the embodiment of FIG. 2 in a gate closedposition;

[0035]FIG. 6 is a sectional view showing a second known metering gate ina partially open position;

[0036]FIG. 7 is a sectional view showing a third known metering gate ina partially open position;

[0037]FIG. 8 is a sectional view showing a fourth known metering gate ina partially open position;

[0038]FIG. 9 is a sectional detail view showing a fifth known meteringgate in a partially open position;

[0039]FIG. 10 is a sectional view showing a sixth known metering gate ina partially open position;

[0040]FIG. 11 is a sectional view showing a seventh known metering gatewith a canted throttle plate bore, in a fully open position;

[0041]FIG. 12 is a view showing the metering gate of FIG. 11 in apartially open position;

[0042]FIG. 13 is a view showing the metering gate of FIG. 11 in a gateclosed position;

[0043]FIG. 14 is a sectional view showing an eighth known metering gatein a fully open position;

[0044]FIG. 15 is a view showing the metering gate of FIG. 14 in apartially open position;

[0045]FIG. 16 is a view showing the metering gate of FIG. 14 in agate-closed position;

[0046]FIG. 17 is a sectional view showing a ninth known metering gate ina fully open position;

[0047]FIG. 18 is a view showing the metering gate of FIG. 17 in apartially open position;

[0048]FIG. 19 is a view showing the metering gate of FIG. 17 in agate-closed position;

[0049]FIG. 20 is a view showing the flow patterns in the metering gateof FIG. 9;

[0050]FIG. 21 is a view showing the flow patterns in the metering gateof FIG. 12;

[0051]FIG. 22 is a top plan view showing an embodiment of a meteringgate constructed according to the present invention in a partially openportion;

[0052]FIG. 23 is a cross-sectional detail view, drawn along lineXXIII-XXIII in FIG. 22;

[0053]FIG. 24 is an enlarged plan view showing the top plate of themetering gate of FIG. 22;

[0054]FIG. 25 is a cross-sectional view, drawn along line XXV-XXV inFIG. 24;

[0055]FIG. 26 is a view showing the embodiment of FIG. 23 in a fullyopen position;

[0056]FIG. 27 is a view showing the embodiment of FIG. 23 in a partiallyopen position;

[0057]FIG. 28 is a view showing the embodiment of FIG. 23 in agate-closed position;

[0058]FIG. 29 is a view showing flow patterns of the metering gate ofFIG. 23;

[0059]FIG. 30 is a top plan view showing another embodiment of ametering gate constructed according to the present invention in apartially open position;

[0060]FIG. 31 is a sectional view, drawn along line XXXI-XXXI in FIG.30;

[0061]FIG. 32 is a sectional view drawn along line XXXII-XXXII in FIG.30;

[0062]FIG. 33 is a view showing the embodiment of FIG. 31 in a fullyopen position;

[0063]FIG. 34 is a view showing the embodiment of FIG. 31 in a partiallyopen position;

[0064]FIG. 35 is a view showing the embodiment of FIG. 31 in agate-closed position;

[0065]FIG. 36 is an enlarged top plan view showing the top plate of themetering gate of FIGS. 30-33;

[0066]FIG. 37 is a sectional view drawn along line XXXVII-XXXVII in FIG.36;

[0067]FIG. 38 is a sectional view, drawn along line XXVIII-XXVIII inFIG. 36;

[0068]FIG. 39 is an enlarged plan view showing the throttle plate of themetering gate of FIGS. 30-33;

[0069]FIG. 40 is a sectional view drawn along line XL-XL in FIG. 39;

[0070]FIG. 41 is a sectional view drawn along line XLI-XLI in FIG. 39;

[0071]FIG. 42 is a view showing flow patterns in the metering gate ofFIG. 31;

[0072]FIG. 43 is a view showing flow patterns in the metering gate ofFIG. 32;

[0073]FIG. 44 is a sectional view showing another embodiment of ametering gate constructed according to the present invention in a fullyopen position;

[0074]FIG. 45 is a view showing the embodiment of FIG. 44 in a partiallyopen position; and

[0075]FIG. 46 is a view showing the embodiment of FIG. 44 in a closedposition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076] The present invention is directed to a metering gate for liquidmetal flow control with reduced clogging, including a top plate thatprovides an offset between one axis of the flow channel in the top plateand the main central axis of the gate.

[0077] Referring to FIGS. 22-28, a first embodiment of the presentmetering gate 1010 includes a well nozzle 1020, a top plate 1030, athrottle plate 1040, a bottom plate 1050, and an outlet tube 1060. Aflow channel bore 1022 in well nozzle 1020 may have a conical section,but other configurations may be used. Flow channel bores 1042 and 1052in throttle plate 1040 and bottom plate 1050 are shown as simplecylinders, but other shapes may be used. Similarly, flow channel bore1062 in outlet tube 1060 is shown as a cylinder, but other shapes may beused.

[0078] As shown in FIG. 23, flow channel bores 1022, 1052 and 1062 ofwell nozzle 1020, bottom plate 1050, and outlet tube 1060, respectively,include central axes 1025, 1055, 1065 which are collinear and define amain central axis 1015. Flow channel bore 1032 of top plate 1030 has aninlet with an inlet axis 1035 that is collinear with the main centralaxis 1015 and an outlet with an outlet axis 1033. Outlet axis 1033 isnot collinear with inlet axis 1035.

[0079] Referring to FIGS. 24 and 25, flow channel bore 1032 in top plate1030 includes an upper shape 1034 and a lower shape 1031. Flow channelbore 1032 is configured with two axes 1033 and 1035, which are notcollinear. The two axes 1033 and 1035 are formed as the result ofsuperpositioning of the two shapes 1031 and 1034. The two shapes 1031and 1034 in top plate 1030 intersect and form one bore 1032 with twoaxes.

[0080] Shape 1034 in top plate 1030 may be a conical section (i.e. asection or frustrum of a cone). Central axis 1035 of shape 1034 ishereinafter referred to as the entry axis 1035 of flow channel 1032 intop plate 1030. Second shape 1031 in top plate 1030 may be a cylindricalsection. Central axis 1033 of shape 1031 is hereinafter referred to asthe outlet axis 1033 of flow channel bore 1032 in top plate 1030. Outletaxis 1033 is parallel to, but not collinear with, entry axis 1035. Thedistance between the two axes 1033 and 1035 is hereinafter referred toas offset 1036.

[0081] Referring to FIG. 23, entry axis 1035 of flow channel bore 1032in top plate 1030 may be arranged so that it is collinear with maincentral axis 1015 of gate 1010. Outlet axis 1033 of top plate 1030,therefore, is offset from main central axis 1015 of gate 1010 in adirection of travel 1044 to open throttle plate 1040. This configurationprovides a less tortuous and more symmetrical flow path when gate 1010is partially open, as shown in FIG. 27, but still provides a relativelystraight downward flow channel 1012 allowing full flow when gate 1010 isfully open, as shown in FIG. 26.

[0082] The advantages of the present invention can be better appreciatedby comparing FIGS. 22 and 23 with FIGS. 1-2. As best seen by comparingFIGS. 1 and 22, rather than main central axis 15 of gate 10 occurring ator near one edge of flow channel 12, main central axis 1015 of gate 1010is more centrally located. Indeed, prior to the present invention, itwas believed that main central axis 15 of gate 10 could only lie at ornear the center of flow channel 12 with gate 10 generally fully open, asshown in FIG. 3. In contrast, the present invention provides forgenerally central location of main central axis 1015 of gate 1010 whengate 1010 is significantly less than fully open, as shown in FIG. 23.Thus, the invention provides a straighter, less tortuous flow path forthe passage of liquid metal when gate 1010 is partially open.

[0083] Referring to FIG. 25, the magnitude of offset 1036 between entryaxis 1035 and outlet axis 1033 of top plate 1030 impacts the amount thatpresent gate 1010 may be opened with a generally centered main centralaxis 1015. Thus, if gate 1010 typically is 65% open when operating, gate1010 may be designed to center main central axis 1015 of gate 1010 inflow channel 1012 when metering gate is 65% open. In other words, thegate 1010 may be configured so that when the gate 1010 is 65% open, themain central axis 1015 is centered with respect to the flow channel. Forexample, the well nozzle 1020 may be offset relative to the exit orificeof the top plate, correspondingly offsetting the central axis 1015relative to the flow channel.

[0084] Referring to FIGS. 26-28, the present metering gate is shown withthrottle plate 1040 in different positions: a fully open gate position(FIG. 26); a partially open gate position (FIG. 27); and a closed gateposition (FIG. 28). As shown in FIG. 28, in the gate closed position theinvention easily allows draining of flow channel 1042 in throttle plate1040 without special drain cuts in the bottom of throttle plate flowchannel 1042 or any requirement for a conical top portion of flowchannel 1052 in bottom plate 1050. This drainage feature results becausethe offset 1036 of outlet axis 1033 relative to the entry axis 1035 oftop plate 1030 inherently moves bottom edge 1037 of flow channel bore1032 in top plate 1030 toward main central axis 1015 of gate 1010. Inother words, because exit orifice 1038 of top plate 1030 is offsetrelative to main central axis 1015, terminating flow through gate 1010requires translating throttle plate 1040 only until entry orifice 1048of throttle plate 1040 ceases to be in fluid communication with shiftedtop plate exit orifice 1038, which occurs before throttle plate exitorifice 1049 ceases to be in fluid communication with flow channel 1052in bottom plate 1050. Thus, when the gate 1010 is closed, flow channelbore 1042 in throttle plate 1040 remains able to drain into flow channel1052 in bottom plate 1050.

[0085] The straighter and more symmetrical nature of the flow in theflow channel 1012 of metering gate 1010 of the present invention, whenit is partially open, is illustrated schematically in FIG. 29. Flow 1071impacts on upper ledge 1047 of throttle plate 1040 (Region A1) and bendstoward opening 1048 of throttle plate 1040. Flow 1072, a second portionof the flow, also is bent, but in the opposite direction from flow 1071,towards opening 1048 as it impacts on entry port 1080 of shape 1034 oftop plate 1030 (Region A2). Thus, the invention promotes two-sidedbending of the flow entering opening 1048 with the bending on each sidebeing towards main central axis 1015 of gate 1010. For this reason, highvelocity jet flow 1073 formed in throttle plate bore 1042 is notstrongly tilted away from main central axis 1015. High velocity jet flow1073 is nearly collinear with main central axis 1015 of gate 1010,thereby achieving a greater degree of flow symmetry.

[0086] Jet flow 1073 does not impinge strongly upon one side of bore1052 in bottom plate 1050, therefore portions of recirculating flows1074, 1075, and 1076 are weaker and less extensive as compared tocorresponding flows in gates not constructed according to the invention.The flow pattern in bottom plate 1050 and outlet tube 1060 is moresymmetrical and spreads more evenly with downward flows 1077, 1078, and1079 occupying a greater portion of flow channel 1052 and 1062 in bottomplate 1050 and outlet tube 1060.

[0087] FIGS. 30-35 show a second embodiment of a metering gate 2010constructed according to the invention, and the flow pattern promotedtherein is illustrated in FIGS. 42 and 43. FIGS. 36-38 show enlargedviews of top plate of 2030 thereof. FIGS. 39-41 show enlarged views ofthe throttle plate 2040 thereof. Throttle plate 2040 has a flow channelbore 2042 with a cross-section defined by an elongated lofted bore.“Lofting” is a term well known by one of reasonable skill in the art ofcomputer-aided design of three-dimensional solids, and is one way toconnect two closed figures, such as a circle, oval or polygon, thatexist on different planes. As used in this application, “loft” impliesno twist.

[0088] Metering gate 2010 incorporates two important features: (1) asshown in FIGS. 36 and 38, an offset 2036 between one axis 2033 of flowchannel bore 2032 in top plate 2030 and main central axis 2015 of gate2010, as described previously with respect to metering gate 1010; and(2) flow channel bores 2032, 2034 (FIG. 36) and 2042 (FIG. 30) of uniquegeometry in top plate 2030 and throttle plate 2040, respectively, whichare narrower in the direction in which throttle plate 2040 moves andelongated in a direction orthogonal thereto. Thus, flow channel bore2032 formed about exit axis 2033 of top plate 2030 and flow channel 2042of throttle plate 2040 are not axisymmetrical, but planar symmetrical,that is, symmetrical with respect to plane 2039. FIGS. 33-35 showmetering gate 2010 in a fully open position (FIG. 33), a partially openposition (FIG. 34) and a closed gate position (FIG. 35).

[0089] Referring to FIGS. 36-38, flow channel bore 2032 in top plate2030 is designed with two non-collinear axis 2033 and 2035 lying in aplane 2036. Axis 2035 is collinear with main central axis 2015. The twoaxis 2033 and 2035 of flow channel 2032 of top plate 2030 are formed asthe result of the superpositioning of two shapes 2031 and 2034. The twoshapes 2031 and 2034 in top plate 2030 intersect, forming one bore 2032with two axis. First shape 2034 in top plate 2030 may be a lofted borewhich has a circular cross-section at the top of plate 2030 thatsmoothly transitions into an elongated cross-section below the top oftop plate 2030. Central axis 2035 of the circular cross-section is theentry axis. Second shape 2031 in top plate 2030 is elongated in adirection orthogonal to plane 2039, i.e. parallel to plane 2038. Centralaxis 2033 of this second shape 2031 is the exit axis. Exit axis 2033 isparallel, but not collinear, with entry axis 2035. The two axis 2033 and2035 define a distance or offset 2036.

[0090] The planar-symmetrical configuration of the top plate and thethrottle plate flow channels reduces the lateral dimension of theopening in the direction of throttle plate movement because the highestdegree of asymmetry in the flow occurs in this direction. Theplanar-symmetrical configuration increases the dimension of the openingin the orthogonal direction because asymmetry is not introduced into theflow in the orthogonal direction. Thus, the present configurationprovides additional straightening of the jet flow formed in flow channel2042 of throttle plate 2040 and further improves the symmetry of theflow in bottom plate 2050 and outlet tube 2060 when gate 2010 ispartially open. This is because, when partially open, the configurationreduces the proportion of the flow that is bent and provides a moresymmetrical bending of this portion of the flow when it approachesopening 2048 of throttle plate 2040. Also, this configuration minimizesthe extent of shelf 2047 above throttle plate 2040 and under-shelfregion 2049 of flow channel 2042 in throttle plate 2040, shown in FIG.35, as compared with shelf 1047 and under-shelf region 1049, shown inFIG. 29, which are critical areas for reducing clogging.

[0091] FIGS. 39-41 show the throttle plate 2040 of the second embodimentof the invention. The throttle plate 2040 has a flow channel 2042 with across-section defined by an elongated lofted bore.

[0092]FIGS. 42 and 43 schematically represent the flow pattern developedin the second embodiment of gate 2010 when partially open. The flowbehavior shown in FIG. 42 is very similar to that in FIG. 29 except thatthe bending of the flow therethrough generally is more symmetrical. Theflow behavior shown in FIG. 43 is symmetrical and uniform with littlebending. As a result of the elongated configuration of flow channels1032 and 1042 in top plate 1030 and throttle plate 1040, respectively, ahigher proportion of flow passes through gate 2010 with little bending.Thus, the flow path is generally straight and there is noover-restriction of the flow with a generally more symmetrical flowreadily developed in outlet tube 2060.

[0093] FIGS. 44-46 show a third embodiment of a metering gate 3010constructed according to the invention. FIGS. 44-46 show metering gate3010 in a fully open position (FIG. 44), a partially open position (FIG.45) and a closed gate position (FIG. 46).

[0094] Referring to FIGS. 44-46, metering gate 3010 has a main centralaxis 3015, and flow channel bore 3032 in top plate 3030 is designed withtwo collinear axis 3033 and 3035. Axis 3033 is the entry axis of topplate 3030 and axis 3035 is the exit axis of top plate 3030. Throttleplate 3040 has a central axis 3037. Bore 3032 in top plate 3030 is asimple straight-through bore.

[0095] Axes 3033 and 3035 are parallel to but offset from main centralaxis 3015. Axes 3033 and 3035 are offset a distance 3036 from maincentral axis 3015.

[0096] Overall, the invention results in less flow restriction and areduction in the rate and extent of clogging as compared with othermetering gates. The recirculating flows are less extensive and weaker,which inhibits the build-up of metallic or non-metallic cloggingmaterial in critical regions of the flow channel, such as the hole orbore of the throttle plate. The improved symmetry of the flow in theoutlet tube improves the uniformity of discharge of liquid metal fromthe outlet tube with a beneficial effect on mold flow behavior and oncast metal quality. Also, impingement of the flow on the sides of theflow channel is less severe and the potential for accelerated refractoryerosion is reduced.

[0097] Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein.

We claim:
 1. An apparatus for metering flow in the continuous casting ofmolten metal including a metering gate, in which the metering gatecomprises: a top plate having a first flow channel bore with an inlethaving an inlet axis and an outlet having an outlet axis; and a throttleplate slidably contacting the top plate and adapted for selectablyreceiving flow from the top plate; characterized in that the inlet axisand the outlet axis are offset.
 2. The apparatus of claim 1, furthercharacterized in that the first flow channel bore is defined bysuperpositioning a plurality of shapes.
 3. The apparatus of claim 2,characterized in that the plurality of shapes are symmetrical and haverespective axes of symmetry.
 4. The apparatus of any one of claims 2 or3, characterized in that the plurality of shapes are selected from agroup consisting of cylindrical shapes, conical shapes and combinationsthereof.
 5. The apparatus of any one of claims 1-4, characterized inthat the offset occurs in an offset direction; and at least one of theplurality of shapes is narrower along the offset direction.
 6. Theapparatus of any one of claims 2-5, characterized in that the pluralityof shapes define an entry port for deflecting flow therethrough.
 7. Theapparatus of claim 6, characterized in that the throttle plate has asecond flow channel bore, the throttle plate being translatable relativeto the top plate along a translation direction generally orthogonal to afluid flowable from the outlet of the first flow channel bore.
 8. Theapparatus of claim 7, characterized in that the throttle plate defines aledge which deflects flow leaving the first flow channel bore, and theentry port and the ledge are adapted to cooperatively bend flow into thesecond flow channel bore.
 9. The apparatus of any one of the claims 7 or8, characterized in that the second flow channel bore is configured toexpand fluid.
 10. The apparatus of any one of the claims 7-9,characterized in that the second flow channel bore is an elongated,lofted bore.
 11. The apparatus of any one of the claims 7-10,characterized in that the second flow channel bore is constricted alongthe translation direction.
 12. The apparatus of any one of the claims7-11, characterized in that the offset occurs along the translationdirection.
 13. The apparatus any one of the claims 7-12, characterizedin that the metering gate further comprises a bottom plate having athird flow channel bore arranged relative to the throttle plate suchthat the third flow channel bore is in fluid communication with thesecond flow channel bore regardless of translation of the throttleplate.
 14. The apparatus of claim 13, characterized in that the thirdflow channel bore includes a third axis that is collinear with the inletaxis.
 15. The apparatus of any one of the claims 7-14, characterized inthat: the second flow channel bore has a second axis; and when thethrottle plate is in an open position, the second axis is collinear withthe outlet axis.
 16. A method for metering flow in the continuouscasting of molten metal comprising: passing fluid into a first flowchannel bore in a first plate of a metering gate in a first verticaldirection; and passing fluid out of the first flow channel bore in thefirst plate in a second vertical direction; characterized by the firstvertical direction being horizontally offset from the second verticaldirection.
 17. The method of claim 16, further characterized by moving asecond plate along a translation direction, the second plate having asecond flow channel bore, relative to the first plate between an openposition, for passing fluid into the second flow channel bore from thefirst passage, and a closed position, for prohibiting the passing offluid into the second flow channel bore from the first flow channelbore.
 18. The method of claim 17, further characterized by passing fluidout of the first flow channel bore by constricting the first flowchannel bore along the translation direction of the moving second plate.19. The method of any one of the claims 17 or 18, further characterizedby expanding the fluid in the second flow channel bore.
 20. The methodof any one of the claims 17-19, further characterized by passing thefluid into a third flow channel bore in a third plate, regardless of theposition of the second plate.
 21. The method of any one of the claims17-20, further characterized by the offset occurring along thetranslation direction of the moving second plate.
 22. The method of anyone of the claims 17-21, further characterized by deflecting the fluidinto the second flow channel bore.
 23. The method of claim 22, furthercharacterized in that the fluid is deflected into the second flowchannel bore by at least one feature selected from the group consistingof a ledge of the second plate, an entry port defined in the first flowchannel bore, and combinations thereof.